Anionic polymerization of conjugated dienes with lithium initiators, such as sec-butyllithium, and hydrogenation of residual unsaturation has been described in many references including U.S. Pat. No. Re. 27,145.
Many times it is desirable to functionalize polymerized conjugated dienes. The capping of living anionic polymers to form functional end groups is described in U.S. Pat. Nos. 4,417,029, 4,518,753, and 4,753,991. Of particular interest for one embodiment of the present invention are anionic polymers that are capped on one or more ends with hydroxyl, carboxyl, phenol, epoxy, or amine groups.
U.S. Pat. No. 5,391,663 describes a polymerization process using a protected functional initiator (PFI) having the structure ##STR1## wherein each R is methyl, ethyl, n-propyl, or n-butyl and A" is an alkyl-substituted or non-substituted propyl bridging group, including --CH.sub.2 --CH.sub.2 --CH.sub.2 --(1,3-propyl), --CH.sub.2 --CH(CH.sub.3)--CH.sub.2 --(2-methyl-1,3-propyl) and --CH.sub.2 --C(CH.sub.3).sub.2 --CH.sub.2 --(2,2-dimethyl-1,3-propyl), or an alkyl-substituted or non-substituted octyl bridging group, including --CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --(1,8-octyl). Cleavage of the silicon-oxygen bond liberates the alcohol group, allowing the facile introduction of hydroxyl functionality at the beginning of the chain. Termination with the appropriate capping agent affords a route to a variety of .alpha.-, .omega.-telechelic polymers.
U.S. Pat. No. 5,416,168 describes a polymerization process using lithium compounds having the structure: ##STR2## wherein A" is cyclohexyl or --CR'R"--, wherein R' is a linear alkyl having from 1 to 10 carbon atoms, and R" is hydrogen or a linear alkyl having from 1 to 10 carbon atoms.
When the PFI initiator is used to prepare telechelic hydrocarbon diols, there are a number of advantages gained by polymerizing isoprene, as opposed, for example, to polymerizing butadiene. The rate of side reactions involving the propagating anion and siloxane species derived from PFIs of structure (2) is slower for isoprene, making the preparation of high functionality diols much easier. The presence of the small amount of mono-functional molecules is a commercial disadvantage compared to available difunctional polymers. Producing polymers with a functionality of greater than 1.90 with butadiene using initiators of structure (2) requires careful control of reaction conditions. Initiators of structure (1) do not suffer from these side reactions, but are much more expensive and more difficult to convert to the desired alcohol (deprotect). Also, there is no need for precise microstructure control to avoid crystallinity in the final, hydrogenated product. However, hydrogenation of the isoprene after polymerization is very difficult. If the standard methanol termination protocol is used, several hundred ppm of Ni/Al catalyst are required to produce hydrogenated products of sufficiently low residual unsaturation. These high catalyst levels result in severe catalyst extraction and effluent treatment problems. When a highly functionalized product is desired, it would be highly desirable to develop a process which increases the ability of the diols, particularly isoprene diols, to be hydrogenated.